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TVS (Transient Voltage Suppressor) Diode Introduction – Difference Between Bidirectional TVS Diode and Unidirectional TVS Diode

release time:2024-03-22Author source:SlkorBrowse:2616

TVS diodes, also known as transient voltage suppressor diodes, are used to absorb surge power and can withstand reverse voltage spikes in a very short period of time. As a result, the voltage between the two poles is clamped at a specific level to prevent subsequent circuits from being affected. In short, they are used for overvoltage protection, which is very common in communication and other products. When connected, they must work in reverse at both ends of the circuit's power supply and ground, similar to a Zener diode, but without the need for a limiting resistor.

Varistors have a similar effect, but the performance of TVS diodes is superior to varistors, especially in terms of reverse conduction time, which is much faster than that of varistors, and the reverse leakage current is also much smaller, allowing for higher permissible operating temperatures.

Under specified reverse application conditions, when subjected to high-energy transient overvoltage pulses, their operating impedance can immediately drop to a very low conducting value, allowing large currents to pass through and clamping the voltage to a predetermined level, effectively protecting delicate components in electronic circuits from damage.

The smallest TVS diode is smaller than a grain of sugar, yet it can discharge up to 20,000 volts! It protects advanced electronic devices such as mobile phones, digital cameras, camcorders, and MP3 players. Its response time is less than half a nanosecond and can respond very quickly to discharged static electricity. This new type of TVS diode can be used not only to manufacture smaller and more complex electronic devices, but also to improve the reliability and quality of products.


TVS diodes can be classified into unipolar and bipolar based on polarity, as well as unidirectional TVS diodes and bidirectional TVS diodes. How to distinguish between them? Unidirectional TVS diodes have a fine color band on one end, which is connected to the positive pole. Bidirectional TVS diodes have two bands in the middle or no markings at all, indicating no polarity.

Bidirectional TVS diodes can absorb transient large pulses in both positive and negative directions and clamp the voltage to a predetermined level. They are suitable for AC circuits, while unidirectional TVS diodes are typically used in DC circuits. Under specified pulse conditions, the maximum peak pulse current allowed by the device. The product of IPP and the maximum clamping voltage Vc(MAX) is the maximum transient pulse power.

The forward characteristics of unidirectional TVS diodes are similar to those of ordinary Zener diodes. The reverse breakdown point for hard breakdown is approximately "right-angled," which is typical of a PN junction avalanche device. The curve segment from the breakdown point to the Vc value indicates that when there is an instantaneous overvoltage pulse, the device's current rapidly increases, the reverse voltage rises to the clamping voltage value, and remains at that level.

When using TVS diodes, it is important to choose the right one so that the rated transient pulse power PPR is greater than the maximum transient surge power that may occur in the protected equipment or circuit. In the region where the device fails, the voltage measured across the device at the specified test current I(BR) is called the breakdown voltage. In this region, the diode becomes a low-impedance path.

Characteristics of bidirectional TVS diodes:


As shown in the diagram, the VI characteristic curve of a bidirectional TVS diode is similar to a combination of two "back-to-back" unidirectional TVS diodes. It exhibits the same avalanche breakdown and clamping characteristics in both positive and negative directions. The relationship is: 0.9 ≤ V(BR) (forward) / V(BR) (reverse) ≤ 1.1. Once the interference voltage applied to both ends exceeds the clamping voltage Vc, it is immediately suppressed. Using TVS diodes in both directions in AC circuits is very convenient.

TVS diodes, also known as transient voltage suppressor diodes, are designed to protect electronic devices from voltage spikes and transient events. They are specialized semiconductor devices that can divert excessive voltage away from sensitive components, thereby safeguarding them from potential damage.

The main difference between bidirectional TVS diodes and unidirectional TVS diodes lies in their ability to handle voltage surges. Bidirectional TVS diodes are capable of conducting in both directions, meaning they can protect against positive and negative voltage transients. On the other hand, unidirectional TVS diodes only conduct in one direction, typically safeguarding against either positive or negative voltage spikes.

Bidirectional TVS diodes offer protection for applications where voltage transients can occur in either direction, such as communication lines and data lines. In contrast, unidirectional TVS diodes are suitable for applications where the voltage surge is expected to come from a specific direction, such as power supply lines.

In summary, bidirectional TVS diodes provide protection against voltage transients in both directions, while unidirectional TVS diodes offer protection in a single specified direction. Both types of TVS diodes play crucial roles in ensuring the reliability and longevity of electronic systems.

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